In recent years, advances in technology, as well as ever evolving tastes in style, have led to substantial changes in the design of automobiles. One of the changes involves the power usage and complexity of the various electrical systems within automobiles, particularly alternative fuel vehicles, such as hybrid, electric, and fuel cell vehicles.
Many of the electrical components, including the electric motors used in electric and hybrid electric vehicles, receive electrical power from alternating current (AC) power supplies. However, the power sources (e.g., batteries) used in such applications provide only direct current (DC) power. Thus, devices known as power inverters are used to convert the DC power to AC power. In addition, double ended inverter topologies can be used to drive a single AC motor with two DC power sources.
High voltage batteries or battery packs are typically used to provide electric power storage for the electric traction systems in most electric and hybrid electric vehicles. Such a high voltage battery may have a nominal voltage of 100 volts or more. Moreover, batteries are utilized to power other onboard subsystems, such as lighting subsystems, instrumentation subsystems, entertainment subsystems, and the like. For example, many electric and hybrid electric vehicles employ traditional subsystems that are powered by a 12 volt battery. Moreover, a vehicle may employ another low voltage system of approximately 42 volts to power intermediate power electrical loads such as an electric power steering subsystem.
For vehicles that utilize more than one voltage level, a device that can transfer energy from one voltage source to another is necessary to maintain desirable charge levels at each source. DC-to-DC converters are commonly used to maintain the charge levels of multiple sources in a hybrid or electric vehicle. A double ended inverter system is able to control state of charge levels between two voltage sources while simultaneously controlling the power delivered to an AC electric motor. However, traditional double ended inverter topologies ideally operate when the two energy sources have similar voltage levels. Therefore, a traditional double ended inverter topology may not operate in an efficient or optimized manner in a hybrid or electric vehicle system having significantly different voltage sources (e.g., 12 volts and 100+ volts).